The present invention relates to a new and improved switchable braking mechanism for braking an individual thread or the like at a related embroidery location in an embroidery machine.
In its more particular aspects, the present invention relates specifically to a new and improved switchable braking mechanism for braking an individual thread at a related embroidery location in an embroidery machine which comprises a linear arrangement or row of embroidery locations. The individual threads extend to related needles and the needles of one row are mounted at a displaceably guided needle carrier. The needles are automatically and individually adjustable by means of related levers between a working position and a rest position in accordance with a programmed control of the embroidery machine. A thread guiding roller is freely rotatably journaled at a roller supporting lever and supplies the thread to the needle operatively associated therewith. Simultaneously with the adjustment of the levers which act on individual needles the related roller supporting levers are pivoted between an operative position and an inoperative position in which the thread guiding rollers are respectively coupled to or decoupled from a common braking member.
It is known to centrally brake the threads of the working needles in order to generate the necessary tension of the threads by means of a brake roller which is common to all embroidery locations of one row of embroidery locations. It is achieved thereby that the advance of the threads is the same at each one of the working or active embroidery locations, particularly independent of the material friction, the tension of the thread between the common brake roller and the bobbin and other possible unequal or irregular conditions at the different individual embroidery locations. Such equal advance of the threads, furthermore, results in an essentially uniform embroidery pattern over all working or active embroidery locations.
There are also known older designs of braking mechanisms in which the threads are wound one or more times around a common brake shaft in order to achieve the braking action. If desired, the common brake shaft can be provided with a friction-increasing cover or lining. Such designs have the disadvantage that the threads which are associated with non-working or deactivated embroidery locations must be disengaged from the common braking shaft. Otherwise such threads would be further supplied in conjunction with the threads of the working or active embroidery locations, but would not be consumed or used. Also, in case of a change in the repeat the threads of previously non-working or deactivated embroidery locations which are re-activated have to be "threaded" again or re-introduced into the related needles. Such operations are complicated and time-consuming.
In more recent constructions of embroidery machines which are provided with so-called color and repeat changing mechanisms selected combinations of working or active and non-working or inactive needles can be switched into their desired positions by the control of the embroidery machine. However, in such embroidery machines the aforementioned thread braking systems can not be employed since, then, the threads would be continuously supplied also to the non-embroidering needles.
To alleviate the aforementioned disadvantages it is known from earlier patents, for example, Swiss Pat. Nos. 28,341, 73,779 and 104,305, to freely rotatably arrange thread guiding rollers at related pivotable roller supporting levers and to associate each one of such thread guiding rollers with a related one of the needles. By pivoting the roller supporting lever the related thread guiding roller can be coupled to in a force- or form-locking manner and decoupled from a common brake shaft, depending upon whether the associated needle is working or at rest. In the arrangement according to the aforementioned Swiss Pat. No. 73,779 each needle in each color and repeat change has to be separately switched into the working or rest position according to the new repeat. In further separate operational steps also the related thread guiding rollers must be individually brought into their corresponding position by pivoting the related roller supporting lever.
In the designs according to the aforementioned Swiss Pat. Nos. 28,341 and 104,305 this time-consuming operation, in the event of a color and/or repeat change, is facilitated by supporting all roller supporting levers at a common adjustment shaft and permitting the same to be selectively connected to the common adjustment shaft for rotation by means of adjustable cams, latches or other similar elements. In this manner, even if by performing a troublesome or time-consuming operation, a distinct combination can be "programmed" so that, by pivoting the adjustment shaft, a number of thread guiding rollers can be simultaneously decoupled from or coupled to the common brake shaft and vice versa. Each time, however, such operation always permits only a single repeat change during which also in this arrangement the needles and the thread guiding rollers have to be "switched" separate from each other.
In case of embroideries which require more frequent repeat and/or color changes the older known arrangements are not only prone to malfunction, but also result in extended downtimes of the embroidery machine due to the frequent and time-consuming switching operations.
Such expense and effort for adjusting the thread guiding rollers is avoided in the arrangement according to Swiss Pat. No. 470,514. In this arrangement the working or active embroidery locations slippingly bring up or draw the required thread length around a stationary brake roller which is provided with friction pads. The thread tension which is generated in this manner can be altered for the entirety of the threads by altering the extent by which the threads are wound up on the braking roller. However, by the use of such so-called slip-tensioning devices high thread tensions cannot be generated. Particularly, it is impossible, using these known arrangements, to block any further advance of the threads. Above all, the specific advantage of the common braking shaft is abandoned by the use of a slip-tension arrangement, namely the advantage of constantly pre-braking all the threads which run at the common braking shaft and thereby ensuring for uniformity of the tension exerted on the different threads. When, however, the individual working or active embroidery locations no longer receive the same amount of the forwardly supplied or advanced threads, but instead receive an amount of thread depending upon the tension of the rearwardly supplied threads, significant differences will result in the produced embroidery from one embroidery location to the other.
Switchable braking mechanisms as known, for example, from Swiss Pat. Nos. 515,372, 535,313 and 616,715, avoid the aforementioned disadvantages in that the rollers which supply threads to the related needles are coupled to or decoupled from the common brake shaft simultaneously with the respective activation and deactivation of the individual embroidery locations.
According to the aforementioned Swiss Pat. No. 515,372 there is provided for this purpose a lever supporting a thread guiding roller and provided with a control arm cooperating with a switching shaft which switches all such levers. The switching shaft is provided in addition to a control shaft acting on the needle bars or rods and is synchronously driven therewith.
In the switchable braking mechanisms according to the aforementioned Swiss Patent Nos. 535,313 and 616,715, an expensive lever or linkage transmission replaces a programmed storage arrangement which takes the form of a control roller or switching roller and which is specifically provided to control the roller supporting levers. By means of the lever or linkage transmission the related thread guiding rollers are coupled to and decoupled from the common brake shaft via the programmed storage arrangement which activates or deactivates the needles at the individual embroidery locations.
The aforementioned known designs have in common the serious deficiency that they possess a large inert mass. Since the threads must be drawn up by the related needle during each stitch for the formation of the loop, the entire system comprising the brake shaft and the thread guiding rollers has to be jerkily incrementally rotated each time by the threads depending on the thread requirements in the known arrangement. Due to currently used high rotational speeds such kind of rotation results in impermissibly high tension peaks in the forwardly supplied threads which actually may make impossible the production of an embroidery of repeats in which only relatively few embroidery locations like, for example, only each sixth embroidery location are working or active at the same time. The reason therefore is that, in view of the small number of threads, the mass which must be jerkily moved by each thread becomes too large.
A further disadvantage inherent in the known systems is the constructionally expensive switching mechanism for engaging and disengaging the individual thread brakes.